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National Water Account 2019

Melbourne: Geographic information

  • The region is home to over 75% of Victoria's population, most of which reside in the Melbourne metropolitan area.
  • Surface water is the main source of water for the region, primarily for urban water supply.
  • Desalinated water is available for urban supply as a climate-independent alternative water source.

 

Map showing the following summary information for the Melbourne region. Water use: 2.5 % of Australia's water use. Land use: 40% of the region used for grazing and agriculture. Ecosystems: 3 Ramsar-listed wetlands with international significance. Water resources: 95% of water is sourced from surface water, mostly for urban supply.

For further geographic information about the region scroll down this page or click on the links below:

 

General description

Area: 11,723 km²
Population: 4.53 million (Australian Bureau of Statistics [ABS] 2016a)

 

Map showing the key water features of the Melbourne region. The Melbourne region is in southeastern Australia and its boundary is defined by four surface water catchments. These are Bunyip River in the southeastern part of the region, Yarra River in the northeast, Maribyrnong River in the northwest, and Werribee River in the west. A small part of the Moorabool River catchment is also in the southwest of the region encompassing the Western Treatment Plant service area.
Figure R1 Contextual map of the Melbourne region

 

  • The Melbourne region is located in the southeast of mainland Australia and is home to more than 75% of Victoria's population.
  • The region is physically defined by the hydrological boundaries of the Bunyip, Yarra, Maribyrnong, and Werribee river catchments, as well as the 105 km² area beyond the Werribee River catchment serviced by the Melbourne Water Western Treatment Plant.
  • About 2.5% of Australia's water use occurs in the region, mostly from surface water for urban supply.

 

Land use

Map showing the distribution and land use types within the Melbourne region. The major urban centre is Melbourne, located in the central part of the region along the coast. Outside of the Melbourne metropolitan area, grazing is the main land use and that occurs throughout the entire region. Areas of conservation and natural environments, as well as dryland agriculture, also occur throughout the region. Smaller areas of forestry occur throughout the northern parts of the region. Mining and irrigated agriculture both occur in the southwest.
Figure R2 Land use in the Melbourne region

 

  • Urban centres make up 23% of the region's total area. The majority of the region's population resides in the Melbourne metropolitan area.
  • 34% of the region is for grazing, which is the dominant land use activity outside of the urban centres.
  • Two irrigation districts, Werribee and Bacchus Marsh, are located in the Werribee catchment and are important vegetable-growing areas for the region (see Irrigation districts).

 

Significant aquatic ecosystems

Map showing the locations of significant wetlands within the Melbourne region. There are three Ramsar-listed wetlands in the region. Edithvale-Seaford Wetlands is about 50 km southeast of Melbourne in the central part of the region near the coast. Western Port Bay wetland is in the southeast of the region. Port Phillip Bay (Western Shoreline) and Bellarine Peninsula is in the southwest of the region, extending further southwest. There are also five nationally-important wetlands: Lerderderg River in the northwest, Werribee-Avalon Area and Point Cook and Laverton Saltworks in the southwest along the coast; Yarra River wetlands in the north; and Mud Islands wetlands, which occurs within the Port Phillip Bay area in the southeast of the region.
Figure R3 Significant wetlands within the Melbourne region

 

  • The region contains several wetland systems of international and national importance, including three Ramsar listed wetlands at Edithvale–Seaford, Western Port Bay, and Western shoreline of Port Phillip Bay.
  • The region also contains five other wetlands of national importance: Lerderderg River, Point Cook and Laverton Saltworks, Werribee–Avalon area, Yarra River wetlands, and Mud Islands wetlands (which occur within Port Phillip Bay).
  • Further information can be found in the Directory of important wetlands in Australia.

 

Water resources

  • Surface water is the main source of water for the region and is primarily used for urban water supply.
  • Groundwater resources are mainly used to support agriculture in the region. Alternative climate-independent water sources for the region include desalinated water and recycled water.

 

Surface water

Storages

Figure R4 Surface water storages in the Melbourne region; capacity of each storage is also shown
Figure R4 Surface water storages in the Melbourne region; capacity of each storage is also shown

 

 

  • Surface water storages are an important water source for both urban supply and irrigation scheme supply.
  • The largest storage in the region is the Thomson Reservoir, which represents 55% of the region's total storage capacity.
  • Thomson Reservoir, located outside the region boundary, supplies water to the Melbourne region's urban water system and, therefore, is considered a surface water asset in the account. Water is transferred from the reservoir to the Upper Yarra Reservoir via the Thomson–Yarra pipeline for distribution to the urban water supply system (see Figure R9).
  • For more information on storages, see the Bureau of Meteorology's Water storage website.

 

Rivers

  • There are four main rivers within the region: Yarra, Bunyip, Maribyrnong, and Werribee rivers.
  • Limited diversions for consumptive use occurs directly from these rivers.

 


Figure R5 Key flow gauging stations along the Bunyip, Yarra, Maribyrnong, and Werribee rivers within the Melbourne region

 

Figure R6 Mean monthly flows along the Werribee, Maribyrnong, Yarra, and Bunyip rivers, and mean monthly rainfall for the Melbourne region
Figure R6 Mean monthly flows along the Werribee, Maribyrnong, Yarra, and Bunyip rivers, and mean monthly rainfall for the Melbourne region

 

 

  • Seasonal flow characteristics of these rivers reflect the local rainfall pattern. Although relatively uniform throughout the year, higher rainfall and streamflow usually occurs during the winter–spring months (June–November); less rainfall and streamflow occurs in summer and autumn.
  • Flows in each of these rivers are affected by flow diversion structures, dam operations, and environmental releases.

 

Groundwater

  • The region's geology can be broadly split into two zones: the northern zone and the southern zone.
  • The geology of the northern zone is typically fractured bedrock and basalt; the coastal southern zone is unconsolidated sediments and basalts.

 

A simplified three-dimensional cross-section image of the Melbourne region's groundwater aquifers. The section is taken along the Werribee River in the southwestern part of the region. The image shows that the region's aquifers are made up of several layered geological formations beneath the Werribee River. The uppermost layer near the coast is the Quaternary sediments. Inland, extending the length of the river, is the Newer volcanic group, Brighton group, Fyansford formation, and Werribee formation (older volcanics). The Werribee formation sits above fresh basement bedrock, as well as a weathered bedrock layer in the upper reaches of the catchment.
Figure R7 Groundwater system within the northern and southern zones of the western part of the Melbourne region

 

  • Groundwater makes up less than 5% of the total water supplied to the Melbourne region.
  • Groundwater is mainly used to supplement surface water sources for high-value agriculture, including production of vegetables, fruits, wine grapes, flowers, and turf.
  • In the Melbourne region, there are six groundwater management areas and three water supply protection areas .

 

Map showing the locations of groundwater management areas within the Melbourne region. There are six groundwater management areas in the region. Lancefield and Merrimu are in the northwest. Cut Paw Paw, Moorabbin, Frankston, and Nepean are along the coast in the central and southern parts of the region. There are three water supply protection areas in the region. Deutgam is in the southwest. Wandin Yallock is in the northeast. Koo Wee Rup occupies a large area in the southeast.
Figure R8 Groundwater management areas within the Melbourne region

 

  • Permissible consumptive volumes, which is the maximum extraction limit, have been defined for each of the region's groundwater management and water supply protection areas.
  • Extraction also occurs in unincorporated areas, which is the rest of the region outside of these designated management areas.

 

Inter-region transfers

  • The Melbourne region's urban water supply is supplemented by surface water transferred from catchments outside of the region.
  • Melbourne's water authorities hold bulk entitlements for water from Lake Eildon (as part of the Goulburn and Murray system) and Silver and Wallaby creeks.

 

Map showing the key features of the inter-region transfer system within the Melbourne region. There are four major pipelines that deliver water from outside of the region to Melbourne's urban system. The Thompson–Yarra Pipeline connects the Thompson Reservoir northeast of the region to the Upper Yarra River in the northeast. The North-South Pipeline connects the Goulburn River to the north with Sugarloaf Reservoir in the central north of the region. A pipeline connects Silver and Wallaby Creeks to the north with Yan Yean Reservoir in the central north of the region. Another pipeline connects the Victorian Desalination Plant, located at Wonthaggi to the south of the region, with Cardinia Reservoir in the central east of the region.
Figure R9 Melbourne's inter-regional water sources; wastewater treatment and desalination plant locations

 

  • Up to 66,000 ML of water may be diverted from Silver and Wallaby creeks into the Melbourne region's storages over a 3-year period.
  • From the Goulburn and Murray systems, up to 75,000 ML of water per year may be diverted (targeted long-term average volume) but only in times of critical human need or when needed for local fire-fighting (Melbourne Water 2014).

 

Desalinated water

  • The Victorian Desalination Plant at Wonthaggi was declared operational in December 2012.
  • Melbourne's three retail water authorities have been granted bulk entitlements to desalinated water produced at the plant. The bulk entitlements allow these authorities to take a total average annual volume of up to 150,000 ML of desalinated water over any period of five consecutive years.
  • For further information on the Victorian Desalination Plant, refer to the Aquasure website.

 

Recycled water

  • There are two large wastewater treatment plants operated by Melbourne Water—Western Treatment Plant and Eastern Treatment Plant—that are the main source of recycled water in the region.
  • The primary uses of treated wastewater include horticulture and pasture irrigation, land and salinity management, and local irrigation (e.g. sport and recreational grounds).
  • About one third of the recycled water produced at the Western Treatment Plant is transferred to Lake Borrie Wetlands.

 

Stormwater

  • There are a number of stormwater harvesting schemes in operation throughout the Melbourne region; however, the volume of water currently harvested is small compared with recycled water.

 

Water systems

Urban water system

Map showing the urban retail and regional water authority service areas within the Melbourne region. There are three major water utilities and two regional water authorities in the Melbourne region. South East Water services the southeastern part of the region, from Melbourne in the centre of the region, extending east and southeast. Yarra Valley Water services the northern, the northeastern and the eastern parts of the region, from Wallan in the north of the region, extending northeast and east. City West Water services the southwestern part of the region, from Melbourne in the centre of the region, extending southwest. Western Water services the western part and the northwestern part excluding area around Ballan of the region, including town centres Bacchus Marsh, Melton, Sunbury and Gisborne. Central Highlands Water services the northwestern part of the region, area around Ballan town centre.
Figure R10 Urban retail and regional water authority service areas within the Melbourne region

 

  • Urban water supply in the Melbourne region is sourced primarily from surface water. Melbourne Water manages and operates the majority of surface water storages throughout the region and is responsible for supplying bulk water to the retail water authorities.
  • Three urban retail water authorities operate exclusively within the Melbourne region—South East Water, Yarra Valley Water, and City West Water—and they source all of their bulk water from Melbourne Water.
  • Western Water and Central Highlands Water are regional water authorities that also operate within the Melbourne region, but their service areas extend beyond the region boundary.

 

Irrigation scheme

Map showing the irrigation areas within the Melbourne region. There are two gazetted irrigation areas in the region, located in the region's west and southwest. The Werribee Irrigation District is located along the coast on the eastern side of the Werribee River. The Bacchus Marsh Irrigation District is, located approximately 40 km northwest of the Werribee Irrigation District around the confluence of the Werribee and Lerderderg rivers.
Figure R11 The Werribee and Bacchus Marsh irrigation districts within the Melbourne region

 

  • Southern Rural Water operates two irrigation areas in the Melbourne region: the Werribee and Bacchus Marsh irrigation districts.
  • Both irrigation districts are important vegetable-growing areas for the region.
  • Water is primarily sourced from Pykes Creek, Merrimu Reservoir, and Melton Reservoir. Recycled water from the Western Treatment Plant is used to supplement the surface water supply.